1. Field the Invention
The present invention provides an improved lockbolt fastener system wherein the lockbolt pin has a threaded portion and at least one axial slot and the collar has a plurality of axially extending grooves in the wall wherein the collar is easily removable after installation, the grooves reducing the collar weight, the collar retaining the load and strength characteristics of conventional lock bolt fastener systems.
2. Description of the Prior Art
Lockbolt fastener systems have been long available in the prior art. For example U.S. Pat. No. 4,472,096 to Ruhl et al describes a conventional lockbolt system as comprising a pin, a collar and two workpieces. The pin has a plurality of lock grooves, the fastener typically being installed by a pull tool grasping the end of the pin, pulling the fastener such that the workpieces are clenched together, the collar then being swaged such that material flows into the pin lock grooves to form an anti-removal lock.
It has become apparent that there is a distinct need to reduce the weight of lockbolt fasteners while retaining the proper strength values. Weight reduction is desirable to the end user, particularly when used in transportation vehicles because it allows increased payload and reduced fuel usage over the lifetime of the vehicle.
In the case of aircraft in addition to the desire of using lightweight components to provide the above advantages, it is desirable that the lockbolt fastener have reduced physical characteristics (profile) for ease of accessibility.
The conventional pin lock grooves function solely to provide an anti-removal lock for the collar, the collar itself having a non-threaded internal bore. When it is necessary to remove the fastener from the workpiece to enable repair or service of aircraft components, for example, the collar must be destroyed in such a manner as to allow it to be removed freely from the pin. This is so because counter rotation torque applied to a collar that not have threads will result only in rotation of the collar but does not allow it to be removed. This procedure is cumbersome, particularly when the fastener is located in an area of restricted accessibility.
What is desired therefore is to provide a lockbolt fastener system which is lighter than those currently available, has a reduced protrusion profile and utilizes a collar that can be easily removed.